The present thesis examines the career of the Andalusian mystic and politician, Ibn Qasi, dwelling particularly on his role as a revolutionary figure in the Almoravid period of Islamic Spain. He was able to achieve much of his popular support by virtue of the esteem in which he was held as a spiritual teacher in the mystical doctrines of Islam, and the present study examines his life as both politician and Sufi. Particular attention has been given to Ibn Qasi's only surviving work, the Eel' an-Na'layn, which has been analysed and partially translated in an attempt to establish his place in the spectrum of Islamic mystical doctrine. The importance of the role played by such men in the political life of Andalusia has long been recognised, and it is the purpose of the present study to give a further precision to the biography of one such leading figure. The transition from Almoravid to Almohad domination in Spain is clarified by isolating, as here, the religious currents which paralleled, and often intermingled with, the patently political objectives.